JavaScript多线程运行库Nexus.js详解(3)

....
/**
 * Creates an input stream from a path.
 * @param path
 * @returns {Promise<ReadableStream>}
 */
async function createInputStream(path) {
 if (path.startsWith('/')) // If it starts with '/', omit it.
  path = path.substr(1);
 if (path.startsWith('.')) // If it starts with '.', reject it.
  throw new NotFoundError(path);
 if (path === '/' || !path) // If it's empty, set to index.html.
  path = 'index.html';
 /**
  * `import.meta.dirname` and `import.meta.filename` replace the old CommonJS `__dirname` and `__filename`.
  */
 const filePath = Nexus.FileSystem.join(import.meta.dirname, 'server_root', path);
 try {
  // Stat the target path.
  const {type} = await Nexus.FileSystem.stat(filePath);
  if (type === Nexus.FileSystem.FileType.Directory) // If it's a directory, return its 'index.html'
   return createInputStream(Nexus.FileSystem.join(filePath, 'index.html'));
  else if (type === Nexus.FileSystem.FileType.Unknown || type === Nexus.FileSystem.FileType.NotFound)
   // If it's not found, throw NotFound.
   throw new NotFoundError(path);
 } catch(e) {
  if (e.code)
   throw e;
  throw new NotFoundError(path);
 }
 try {
  // First, we create a device.
  const fileDevice = new Nexus.IO.FilePushDevice(filePath);
  // Then we return a new ReadableStream created using our source device.
  return new Nexus.IO.ReadableStream(fileDevice);
 } catch(e) {
  throw new InternalServerError(e.message);
 }
}
/**
 * Connections counter.
 */
let connections = 0;
/**
 * Create a new HTTP server.
 * @type {Nexus.Net.HTTP.Server}
 */
const server = new Nexus.Net.HTTP.Server();
// A server error means an error occurred while the server was listening to connections.
// We can mostly ignore such errors, we display them anyway.
server.on('error', e => {
 console.error(FgRed + Bright + 'Server Error: ' + e.message + '\n' + e.stack, Reset);
});
/**
 * Listen to connections.
 */
server.on('connection', async (connection, peer) => {
 // Start with a connection ID of 0, increment with every new connection.
 const connId = connections++;
 // Record the start time for this connection.
 const startTime = Date.now();
 // Destructuring is supported, why not use it?
 const { request, response } = connection;
 // Parse the URL parts.
 const { path } = parseURL(request.url);
 // Here we'll store any errors that occur during the connection.
 const errors = [];
 // inStream is our ReadableStream file source, outStream is our response (device) wrapped in a WritableStream.
 let inStream, outStream;
 try {
  // Log the request.
  console.log(`> #${FgCyan + connId + Reset} ${Bright + peer.address}:${peer.port + Reset} ${
   FgGreen + request.method + Reset} "${FgYellow}${path}${Reset}"`, Reset);
  // Set the 'Server' header.
  response.set('Server', `nexus.js/0.1.1`);
  // Create our input stream.
  inStream = await createInputStream(path);
  // Create our output stream.
  outStream = new Nexus.IO.WritableStream(response);
  // Hook all `error` events, add any errors to our `errors` array.
  inStream.on('error', e => { errors.push(e); });
  request.on('error', e => { errors.push(e); });
  response.on('error', e => { errors.push(e); });
  outStream.on('error', e => { errors.push(e); });
  // Set content type and request status.
  response
   .set('Content-Type', mimeType(path))
   .status(200);
  // Hook input to output(s).
  const disconnect = inStream.pipe(outStream);
  try {
   // Resume our file stream, this causes the stream to switch to HTTP chunked encoding.
   // This will return a promise that will only resolve after the last byte (HTTP chunk) is written.
   await inStream.resume();
  } catch (e) {
   // Capture any errors that happen during the streaming.
   errors.push(e);
  }
  // Disconnect all the callbacks created by `.pipe()`.
  return disconnect();
 } catch(e) {
  // If an error occurred, push it to the array.
  errors.push(e);
  // Set the content type, status, and write a basic message.
  response
   .set('Content-Type', 'text/plain')
   .status(e.code || 500)
   .send(e.message || 'An error has occurred.');
 } finally {
  // Close the streams manually. This is important because we may run out of file handles otherwise.
  if (inStream)
   await inStream.close();
  if (outStream)
   await outStream.close();
  // Close the connection, has no real effect with keep-alive connections.
  await connection.close();
  // Grab the response's status.
  let status = response.status();
  // Determine what colour to output to the terminal.
  const statusColors = {
   '200': Bright + FgGreen, // Green for 200 (OK),
   '404': Bright + FgYellow, // Yellow for 404 (Not Found)
   '500': Bright + FgRed // Red for 500 (Internal Server Error)
  };
  let statusColor = statusColors[status];
  if (statusColor)
   status = statusColor + status + Reset;
  // Log the connection (and time to complete) to the console.
  console.log(`< #${FgCyan + connId + Reset} ${Bright + peer.address}:${peer.port + Reset} ${
   FgGreen + request.method + Reset} "${FgYellow}${path}${Reset}" ${status} ${(Date.now() * startTime)}ms` +
   (errors.length ? " " + FgRed + Bright + errors.map(error => error.message).join(', ') + Reset : Reset));
 }
});

/**
 * IP and port to listen on.
 */
const ip = '0.0.0.0', port = 3000;
/**
 * Whether or not to set the `reuse` flag. (optional, default=false)
 */
const portReuse = true;
/**
 * Maximum allowed concurrent connections. Default is 128 on my system. (optional, system specific)
 * @type {number}
 */
const maxConcurrentConnections = 1000;
/**
 * Bind the selected address and port.
 */
server.bind(ip, port, portReuse);
/**
 * Start listening to requests.
 */
server.listen(maxConcurrentConnections);
/**
 * Happy streaming!
 */
console.log(FgGreen + `Nexus.js HTTP server listening at ${ip}:${port}` + Reset);